A common pesticide may be a menace to pollinators. Know how to protect them.

Many homeowners want to throw a lifeline to beleaguered bees and butterflies by planting pollinator gardens that will provide sustenance and habitat, but the unwitting use of insecticides may lure these beloved insects to their doom.

The worry is that a common type of pesticide known as neonicotinoids, or neonics, will poison honeybees, bumblebees, monarch butterflies — all the species of insects that we want in our gardens.

For a decade, neonics have dominated a frustrating quest to find a cause for the loss of commercial beehives in agriculture, but the issue has also moved into the garden, particularly with new legislation in Maryland. If the Pollinator Protection Act is signed into law by Gov. Larry Hogan this month, consumers will not be able to buy neonic insecticides after 2017. Farmers and licensed applicators could still use them.

The pesticide industry says neonics are safe, that honeybees are doing all right and that the law “inexplicably blames homeowners for the nonexistent decline in bees.” But those who want to see broader restrictions for neonics in the United States are buoyed by it. Hogan has yet to announce whether he will sign the bill.

“It’s important that Maryland be the leader and show the rest of the United States these are really harmful compounds and we need to limit their use,” said April Boulton, associate professor of biology at Hood College in Frederick. She was among scientists testifying for the bill earlier this year.

Neonics control some of the most common and persistent garden pests, including thrips, adelgids, borers, scale insects and Japanese beetles, but they also kill or harm beneficial insects, as well as aquatic life if they enter bodies of water. Within a treated plant, the compounds also find their way to pollen and nectar, the treats that flowers give pollinators for their service.

One of the major concerns is that homeowners, as opposed to farmers or professional landscapers, are the least likely to know what’s in a pesticide product and correctly follow the label’s directions.

“Instead of putting in a capful in a bucket of water, the homeowner will pour in half the bottle or the whole bottle,” with highly toxic results, Boulton said.

But Boulton and many other scientists say that even at correct doses, the compounds can harm desirable organisms, even if they don’t kill them. Hartmut Doebel, assistant professor of biology at George Washington University, has directed honeybee experiments that suggest memory loss with extremely low levels of imidacloprid, he said. Bees need memory to navigate between nectar sources and their hives. Imidacloprid is one of the most common types of neonics; others include acetamiprid, clothianidin and dinotefuran. (These are the names consumers have to find in fine print on the bottle labels to know whether they contain neonics.)

“Even at sublethal levels, they have impairments of memory capacities,” he said. “We are not aware of all the implications and effects” of the insecticides.

Doebel and others said that most of the research on neonic toxicity has been on honeybees, because of their agricultural importance, and much less is known of the effects on other insects, including hundreds of species of native bees that are much harder to track.

To discover whether a pesticide contains a neonicotinoid, look for the active ingredient on the label. The most common neonic is imidacloprid, but others include thiacloprid, acetamaprid, clothianidin and dinotefuran. (Gaby D'Alessandro/for The Washington Post)

This was a central argument by environmental groups commenting on a current draft assessment of imidacloprid by the Environmental Protection Agency. (A preliminary review says honeybees feeding on two crops — citrus and cotton — have been placed at risk from neonics.)

“In our home gardens, we have an amazing array of beneficial insects — lacewings, assassin bugs, for example — that help us maintain pest levels,” said Aimee Code, pesticide program director at the Xerces Society for Invertebrate Conservation. “Neonics can be extremely harmful, particularly because they are so long-lived and toxic.”

Neonics entered the market in the 1990s and were quickly embraced by farmers around the world: They were cheap, effective, long-lasting and safe for people and other warm-blooded animals, which was not the case for older-generation pesticides, including ones made from real nicotine.

As a systemic insecticide, neonics are taken up within a plant’s tissues. This proved a seemingly perfect way of targeting the aphids, flea beetles, weevils, worms or whatever pest was sucking the sap or munching on the leaves. Even if you just treated a seed with a neonic, it would grow into a plant fully protected from pests.

Stephanie Darnell, a scientist with Bayer Crop Science, said that restricting a systemic pesticide such as neonics, which her company produces, could lead consumers to use more products that are less discriminating in what they kill. The Maryland bill could also push consumers, she said, to pay for lawn service agreements with contractors with licenses to use neonics.

By 2011, almost one-third of insecticides used globally were neonics, creating a market worth $3.6 billion.

By then, the mysterious loss of honeybees known as colony collapse disorder had emerged to bring unsustainable hive losses to commercial beekeepers, and researchers began to link the crisis to the widespread use of neonics.

The jury is still out on the cause of the disorder, which is more likely to be a lethal mix of stressors, particularly the spread of a parasitic bee mite. Some studies show that neonics compromise bees’ immune systems and ability to raise their young.

In spite of the absence of a clear single reason, the movement against neonics appears to be gaining traction. The European Union has imposed a ban on three types of neonics pending study. In the United States, the EPA has put a halt on issuing permits for new neonic pesticide products and is reevaluating the environmental risks of neonics. Several states besides Maryland are considering restrictions, and major retailers such as Lowe’s and Home Depot have said they will phase out the sale of neonic pesticides and label plants that have been treated. Ortho recently announced it was removing neonics from eight consumer pesticides.

One quandary for gardeners is knowing whether annuals, perennials or even woody plants sold at garden centers have been treated with neonics, which can linger in a plant for a year or more, as well as in the soil. It’s also a challenge for independent garden centers, which might source a wide range of plants from dozens of different growers.

Retail nursery Behnke in Beltsville has pulled neonic pesticides from its shelves, stopped treating its plants with neonics and polled its growers on neonic use. “About 70 percent of the perennial growers we buy from are not using them,” horticulturist Larry Hurley said. Plants sold by Behnke’s as “pollinator-friendly” are known not to be treated, he said.

My thoughts? I wouldn’t want neonic-treated plants in my suburban garden, given the risks to bees. I could see using a neonic on a precious hemlock to ward off the woolly adelgid (as a conifer, the hemlock wouldn’t attract pollinators). If I had a specimen ash tree, now at mortal risk from the emerald ash borer, the choice would be hard, although ash trees aren’t known as big magnets for insect pollinators, so it might be justified. I would never treat trees that are bee magnets, such as tulip trees, linden trees, cherries and hollies, and fruit trees, to name just a few obvious ones.

The bigger issue is the idea of reaching for a pesticide to fix a problem, which is often a symptom of something greater. Most problems can be minimized by picking a plant developed by nature or a breeder to grow in our region, to place it correctly, to care for the soil and to live with a level of insect or disease damage. Weeds are suppressed by the presence of more plants and by the gardener with a sharp hoe.

“We need to take a step back,” said Scott Black, executive director of the Xerces Society and the co-author of “Gardening for Butterflies.” “We need to work with nature rather than fighting against it.”

Adrian HigginsAdrian Higgins has been writing about gardening, landscape design and related environmental topics since the late 1980s. He joined The Washington Post in 1994. He is the author of several books, including the "Washington Post Garden Book" and "Chanticleer, a Pleasure Garden." Follow